"The eggs from which they are produced, are deposited in the sands or dust; where they lie until rain falls, and causes the herbage to spring up.

Then the locusts are hatched, and in their first stage are supported upon this herbage.

When it becomes exhausted, they are compelled to go in search of food.

Hence these `migrations,' as they are called." This explanation seemed clear enough.
"Now I have heard," said Hendrik, "of farmers kindling fires around their crops to keep off the locusts.

I can't see how fires would keep them off--not even if a regular fence of fire were made all round a field.